Underwater breathing devices such as snorkels and regulators include mouthpieces which are retained in the mouth of the user and which prevent the ambient water from entering the mouth of the person using the device while permitting the free flow of gases through the mouthpiece to and from the mouth of the user.
The prior art mouthpieces have ordinarily been made of a flexible material such as rubber or plastic and include a lip flange which surrounds the opening through the mouthpiece through which the breathing gases pass. This flange is in the form of a flexible curved surface that fits between the lips and the outer frontal surface of the user's teeth to effect a seal between the ambient and the mouth of the user. The most common prior art mouthpieces further include a pair of lugs which extend from the flange on opposite sides of the breathing opening and are adapted to fit between the biting surfaces of the upper and lower teeth of the user. The user thus bites down onto the lugs to hold the mouthpiece in place within his mouth. Since the retainer lugs must be gripped firmly by the teeth over long periods of time in order to prevent dislodging of the mouthpiece, it is critical that the mouthpiece be comfortably held in the mouth of user. Indeed, in some cases the user's jaw might be damaged from a prolonged or excessively unnatural bite with the jaw bones unseated.
This problem has been recognized for many years and various solutions to it have been suggested. Accordingly, mouthpieces designed to reduce fatigue have been placed on the market. For example, one type of mouthpiece employs thermoplastic lug surfaces which are customized to have a shape complimentary to the shape of the biting surfaces of the teeth of the user (see U.S. Pat. No. 4,136,689 where one such mouthpiece construction is described). In another proposed solution to the problem the upper and lower halves of the mouthpiece are nonsymmetrical so as to conform to the natural overbite of a normal human jaw. Still another proposed solution was to replace the lip flange with a cup housing which was disposed externally of the mouth and sealed against the face of the user throughout a continuous area surrounding his mouth. Such a device is disclosed in U.S. Pat. No. 4,031,888.